A simple limited cpio implementation for packing and unpacking initramfs
images. Unlike the original cpio, it is file-oriented, with mpac-like
command syntax. And just like mpac, it's got the `pack` command for
plucking individual files from the filesystem into the archive.

The kernel only accepts the "ascii cpio", so that's the only format this
tool supports. No support for "binary cpio", no support for tar.
